Modern electronic equipment such as televisions, telephones, radios and computers are generally constructed of solid state devices. Solid state devices are preferred in electronic equipment because they are extremely small and relatively inexpensive. Additionally, solid state devices are very reliable because they have no moving parts, but are based on the movement of charge carriers.
Solid state devices may be transistors, capacitors, resistors and other semiconductor devices. Typically, such devices are fabricated on a substrate and interconnected to form memory arrays, logic structures, timers and other components of an integrated circuit. One type of memory array is a dynamic random access memory (DRAM) in which memory cells can retain information only temporarily and must be refreshed at periodic intervals. Despite this limitation, DRAMs are widely used because they provide low cost per bit, high device density and feasibility of use.
In a DRAM, each memory cell typically includes an access transistor coupled to a storage capacitor. The memory cells are accessed by a series of word and bit lines connected to the access transistor. The word lines control the access transistors to allow the bit lines to read data into and out of the storage capacitors.
To reduce the cost of manufacturing DRAMs, multiple contact patterns have been used to form bit line contacts between a bit line and an access transistor and storage node contacts between an access transistor and a storage capacitor. Thus, separate masking processes are not needed for the bit line and storage node contacts. Multiple contact patterns, however, are typically complex due to the density and configuration of the DRAM cells. This complexity leads to difficulty in manufacturing and inspecting the patterns.